In vertebroplasty, the surgeon seeks to treat a compression fracture of a vertebral body by injecting bone cement such as PMMA into the fracture site. In one clinical report, Jensen et al., AJNR: 18 Nov. 1997, Jensen describes mixing two PMMA precursor components (one powder and one liquid) in a dish to produce a viscous bone cement; filling 10 ml syringes with this cement, injecting it into smaller 1 ml syringes, and finally delivering the mixture into the desired area of the vertebral body through needles attached to the smaller syringes.
U.S. Pat. No. 6,348,055 (“Preissman”) reports that the use of syringes to deliver bone cement in vertebroplasty procedures leads to high pressure spikes. Preissman discloses using a screw-type high pressure injection device to provide an even injection pressure during delivery of the bone cement.
Despite the relative success of vertebroplasty, there have been reports of complications such as embolisms. For example, Padovani, Am.J. Neuroradiol. 20: 375–377, March 1999, reports on a pulmonary embolus of acrylic cement found in a patient after percutaneous vertebroplasty, and suggests that the embolism may have been caused by insufficient polymerization of the PMMA at the time of injection. Padovanni recommends adequate preparation of the bone cement and the use of biplane fluoroscopy as a means to lower the incidence of embolisms.
Amar, Neurosurgery, Vol. 49, No. 5, November 2001, also examined the issue of embolisms in vertebroplasty procedures and reports that some have suggested that needle placement near the geographic center of the vertebral body may increase the risk of pulmonary embolism or epidural compression, inasmuch as paravertebral and basivertebral veins frequently anastomose at that site.
Scroop, Am.J. Neuroradiol. 23:868–870, May 2002 provides a case report of a cerebral embolism during intraoperative vertebroplasty, and discusses both PMMA and fat embolisms. Scroop recommends that a maximum of three levels of vertebral bodies be treated in a single setting.
In sum, none of the art directed to vertebroplasty suggests removing fat or bone marrow prior to cement injection as a way of reducing embolisms.
U.S. Pat. No. 5,108,404 (“Scholten”) discloses inserting an inflatable device within a passage within the vertebral body, inflating the balloon to compact the cancellous bone and create an enlarged void, and finally injecting bone cement into the void. Scholten further dicloses inserting an irrigation nozzle into the vertebral body after removing the balloon and irrigating the void with normal saline. See column 7, lines 36–40). Scholten further discloses injecting the bone cement through a double-barreled injection gun having a cement delivery tube and an aspirating tube that aspirates constantly. See column 7, lines 42–50).
Hip arthroplasty has long been concerned with pulmonary embolisms from fat and bone marrow. For example, U.S. Pat. No. 5,558,646 (“Roche”) discloses that one conventional technique for managing the embolism problem is surgical lavage which include using an irrigating fluid to dislodge fat, marrow and debris, using suction to remove the dislodged soft tissue. Roche further suggests the use of hemostatic agents in such procedures. Pitto, Clin. Orth. Rel. Res. 355 (1998), pp. 23–34, discloses that the logical prophylactic measure to prevent intravasation of fat and bone marrow is to create sufficient drainage, and further suggests providing venting holes to reduce intramedullary pressure. However, none of the hip arthroplasty publications discussed above suggest that their techniques for lowering the incidence of embolisms should be applied to vertebroplasty.
Therefore, there is a need to improve the safety of the vertebroplasty, and in particular to reduce the frequency and severity of pulmonary embolism in vertebroplasty procedures.